Partial flow cell

ABSTRACT

A partial flow cell may include a cathode chamber, an anode chamber, and a separator arrangement sandwiched between the cathode and anode chambers. The separator arrangement may be configured to permit ionic flow between electroactive materials disposed within the cathode and anode chambers. One of the cathode and anode chambers may be configured to permit an electroactive material to flow through the chamber during operation. The other of the cathode and anode chambers may be configured to hold an electroactive material fixed within the chamber during operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 13/102,566,filed May 6, 2011, the disclosure of which is incorporated in itsentirety by reference herein.

TECHNICAL FIELD

This disclosure relates to electrochemical cells.

BACKGROUND

A typical electrochemical cell may include a cathode side and anode sideseparated by a separator arrangement. The cathode side may include acathode current collector, a cathode electroactive material (reduced ondischarge) and an electrolyte. The anode side may include an anodecurrent collector, an anode electroactive material (oxidized ondischarge) and an electrolyte. The separator arrangement separating thecathode and anode sides, inter alia, permits ionic flow therebetween.The current collectors, electroactive materials, electrolytes andseparator arrangement thus form an electrochemical reactor that convertschemical energy to electricity. Hence, the current collectors may be(externally) electrically connected together to form an electricalcircuit.

In this context, the electrochemical reactor is an electrochemical cellwithin which the cathode electroactive material and anode electroactivematerial do not flow into and/or out of the electrochemical reactorduring operation: they are fixed.

SUMMARY

A partial flow cell may include a cathode current collector, a catholytein contact with the cathode current collector, a separator arrangementin contact with the catholyte, and a fixed anode active material incontact with the separator arrangement. The catholyte may include acathode active material. The separator arrangement may permit ionic flowbetween the cathode active material and fixed anode active material. Thepartial flow cell may further include an anode current collector incontact with the fixed anode active material and configured to beexternally electrically connected with a cathode current collector.

A partial flow cell may include an anode current collector, an anolytein contact with the anode current collector, a separator arrangement incontact with the anolyte, and a fixed cathode active material in contactwith the separator arrangement. The anolyte may include an anode activematerial. The separator arrangement may permit ionic flow between theanode active material and fixed cathode active material. The partialflow cell may further include a cathode current collector in contactwith the fixed cathode active material and configured to be externallyelectrically connected with an anode current collector.

A partial flow cell may include a cathode chamber, an anode chamber, anda separator arrangement sandwiched between the cathode and anodechambers. The separator arrangement may be configured to permit ionicflow between electroactive materials disposed within the cathode andanode chambers. One of the cathode and anode chambers may be configuredto permit an electroactive material to flow through the chamber duringoperation. The other of the cathode and anode chambers may be configuredto hold an electroactive material fixed within the chamber duringoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a flow cell system.

FIG. 2 is a schematic diagram of a partial flow cell system.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

A flow cell is a type of rechargeable cell in which electrolytecontaining one or more dissolved electroactive species flows through(into and out of) an electrochemical reactor that converts chemicalenergy to electricity. Additional electrolyte containing one or moredissolved electroactive species is stored externally, generally intanks, and is usually pumped through the electrochemical reactor (orelectrochemical reactors). A flow cell may thus have variable capacitydepending on the size of the external storage tanks

Referring to FIG. 1, a flow cell 10 may include a cathode side 12 and ananode side 14 separated by a separator 16 (e.g., an ion exchangemembrane). The cathode side 12 includes a cathode chamber 18, cathodecurrent collector 20 and catholyte reservoir 22. Likewise, the anodeside 14 includes an anode chamber 24, anode current collector 26 andanolyte reservoir 28. The separator 16 permits ionic flow betweenelectroactive materials in the cathode and anode chambers 18, 24. Thechambers 18, 24, current collectors 20, 26 and separator 16 thus form anelectrochemical reactor 29 that converts chemical energy to electricity(and, in certain arrangements, electricity to chemical energy). As such,the cathode 20 and anode 26 may be (externally) electrically connected(together or with other anodes and cathodes respectively) to form anelectrical circuit.

Catholyte 30 and anolyte 32 typically combine an electrolyte used totransport ions with cathode and anode reactive materials, respectively,through soluble intermediates. The catholyte 30 and anolyte 32 arecirculated on respective sides of the cell 10 to drive the reactionwithin the electrochemical reactor 29. Hence, the catholyte 30 andanolyte 32 are mobile. To that end, the cathode side 12 further includesinlet/outlet pipes 34 in fluid communication with the cathode chamber 18and catholyte reservoir 22, and circulation pump 36, heat exchanger 38and valves 40 each operatively arranged with the inlet/outlet pipes 34.The circulation pump 36, as the name suggests, circulates the catholyte30 through the cathode chamber 18, catholyte reservoir 22 andinlet/outlet pipes 34. The heat exchanger 38 may be operated to controlthe temperature of the catholyte 30. The valves 40 may be operated tocontrol the flow of catholyte 30 into and/or out of the cathode chamber18.

The anode side 14 includes inlet/outlet pipes 42, circulation pump 44,heat exchanger 46 and valves 48. The inlet/outlet pipes 42 are in fluidcommunication with the anode chamber 24 and anolyte reservoir 28, andcirculation pump 44, heat exchanger 46 and valves 48 each operativelyarranged with the inlet/outlet pipes 34. The circulation pump 44circulates the anolyte 32 through the anode chamber 24, anolytereservoir 28 and inlet/outlet pipes 42. The heat exchanger 46 may beoperated to control the temperature of the anolyte 32. The valves 48 maybe operated to control the flow of anolyte 32 into and/or out of theanode chamber 24.

The anode side 14 may include a slurry of ZnO and NaOH mixed in theanolyte reservoir 28 to ensure maximum dissolution of active material(zincate) in the solution. This solution may be used as the anolyte 32for the flow cell 10. On charge, the soluble zincate is reacted at thesurface of the anode 26 to deposit Zn metal on the anode surfaceadjacent to the anode chamber 24. On discharge, a load reverses thereaction oxidizing the Zn metal off the surface of the anode 26. Thezincate species is only marginally soluble in the anolyte 32 so themajority of the discharged material precipitates as ZnO. This dischargeproduct is normally stored in the reservoir 28 but should be managed toensure it does not deposit elsewhere in the system and possibly plugflow channels or mask surface area changing the current distribution.

A controller (not shown) may operate the circulation pumps 36, 44 andvalves 40, 48 to flow the catholyte 30 and anolyte 32 into and out ofthe chambers 18, 24 and reservoirs 22, 28 respectively. Such flow oftenrequires sophisticated flow and temperature controls. With multiplecells (as in a battery), a typical flow system may become morecomplicated because the same reservoir may be used for the multiplecells. The use of a single reservoir with multiple cells may result inan ionic path between cells. Because the cells are typically connectedelectrically from cell to cell, this ionic connection may introduce aself discharge or loss of usable energy over time. Engineering fixes forthis issue can be complicated and may require complex methods ofisolation including multiple reservoirs, long connection lengths tocells, mechanical isolation by valves, draining the system between uses,etc.

Referring to FIG. 2 in which like numbered elements may share similardescriptions, a partial flow cell 150 may include a cathode side 112 andan anode side 152 separated by separators 116, 153, 154, which are incontact with each other. The cathode side 112 may include a cathodechamber 118, cathode current collector 120 and catholyte reservoir 122.The cathode chamber 118, in this example, is partially defined by theseparator 116 and cathode current collector 120. The anode side 152 mayinclude an anode chamber 156 and anode current collector 158. The anodechamber 156, in this example, is partially defined by the separator 154and anode current collector 158. The separators 116, 153, 154, interalia, permit ionic flow between electroactive materials in the cathodechamber 118 and anode chamber 156. The chambers 118, 156, cathode 120,anode 158, and separators 116, 153, 154 thus form an electrochemicalreactor 160 that converts chemical energy to electricity (and, incertain arrangements, electricity to chemical energy). As such, thecurrent collectors 120, 158 may be (externally) electrically connected(together or with other anodes and cathodes respectively) to form anelectrical circuit.

As explained above, catholyte 130 typically combines an electrolyte usedto transport ions with cathode reactive materials through solubleintermediates. The catholyte 130 is circulated on the cathode side 112of the cell 150 to drive the reaction within the electrochemical reactor160. Hence, the catholyte 130 is mobile. The cathode side 112 thusincludes inlet/outlet pipes 134 in fluid communication with the cathodechamber 118 and catholyte reservoir 122, and circulation pump 136, heatexchanger 138 and valves 140 each operatively arranged with theinlet/outlet pipes 134. The circulation pump 136 circulates thecatholyte 130 through the cathode chamber 118, catholyte reservoir 122and inlet/outlet pipes 134. The heat exchanger 138 may be operated tocontrol the temperature of the catholyte 130. The valves 140 may beoperated to control the flow of catholyte 130 into and/or out of thecathode chamber 118.

Anode electroactive material 162 disposed within the anode chamber 156,in the example of FIG. 2, includes a Zn/ZnO matrix of active materialwith binders, modifiers and conductive additives pasted onto the anodecurrent collector 158 and in contact with the separator 154. This Znelectrode will then provide the following half cell charge and dischargereactions:

Other matrices of active materials, binders, modifiers and conductiveadditives may also be used. For example, a Cd/Cd(OH)₂ matrix of activematerial (and associated binders, modifiers and conductive additives) orany other suitable metal/metal oxide or metal/metal hydride matrix ofactive material may be used.

The separator 116 may be an ion exchange membrane, the separator 153 maybe a nonwoven or woven matt, and the separator 154 may be a microporoussheet. The nonwoven matt 153 retains the anode side electrolyte. Themicroporous sheet 154 prevents migration of the anode electroactivematerial 162 from the anode chamber 156 to the nonwoven matt 153. Agreater or fewer number of separators, however, may be used depending onthe electrochemistry of the electroactive materials within the reactor160. For example, a cadmium based anode may require only a nonwoven orwoven matt to retain electrolyte since the cadmium reaction is a solidstate reaction. Other arrangements are also possible.

As apparent to those of ordinary skill, the anode electroactive material162 does not flow into and/or out of the anode chamber 156: it is fixed(it is not mobile). In other words, the anode electroactive material 162is stationary and held within the anode chamber 156. Because the anodeelectroactive material 162 is not circulated on the anode side 114 ofthe cell 150, the anode side 114 need not include a reservoir andassociated inlet/outlet pipes, circulation pump, heat exchanger andvalves; simplifying the construction and control of the cell 150. (Thecapacity of the cell 150, however, may be limited by the size of theanode chamber 156.)

A partial flow cell, in other embodiments, may include an anode sideconfigured similarly to that described with respect to FIG. 1 and acathode side configured equivalently to the anode side 152. That is,such a cathode side may include a cathode adjacent to a cathode chamberhaving a fixed cathode electroactive material (e.g.,Ni(OH)_(2/NiOOH, Ag/Ag) ₂O, etc.) disposed therein. A separatorarrangement including an ion exchange membrane and a nonwoven or wovenmatt to retain electrolyte may separate the anode and cathode sides,etc.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

1. A partial flow cell comprising: a cathode current collector; a mobilecatholyte including a cathode active material, the catholyte in contactwith the cathode current collector; a separator arrangement in contactwith the catholyte; a fixed anode active material in contact with theseparator arrangement, the separator arrangement permitting ionic flowbetween the cathode active material and fixed anode active material; andan anode current collector in contact with the fixed anode activematerial and configured to be externally electrically connected with acathode current collector.
 2. The cell of claim 1 wherein the separatorarrangement includes a nonwoven or woven matt configured to retainelectrolyte.
 3. The cell of claim 2 wherein the separator arrangementfurther includes a microporous sheet in contact with the nonwoven orwoven matt and the fixed anode active material and configured to preventmigration of the fixed anode active material into the nonwoven or wovenmatt.
 4. The cell of claim 1 wherein the separator arrangement includesan ion exchange membrane in contact with the catholyte.
 5. The cell ofclaim 1 wherein the catholyte is a liquid or liquid slurry.
 6. The cellof claim 1 wherein the fixed anode active material is a paste.
 7. Thecell of claim 1 wherein the fixed anode active material comprises ametal/metal oxide or metal/metal hydroxide matrix.
 8. The cell of claim1 wherein the fixed anode active material comprises zinc/zinc oxide. 9.A partial flow cell comprising: an anode current collector; a mobileanolyte including an anode active material, the anolyte in contact withthe anode current collector; a separator arrangement in contact with theanolyte; a fixed cathode active material in contact with the separatorarrangement, the separator arrangement permitting ionic flow between theanode active material and fixed cathode active material; and a cathodecurrent collector in contact with the fixed cathode active material andconfigured to be externally electrically connected with an anode currentcollector.
 10. The cell of claim 9 wherein the separator arrangementincludes a nonwoven or woven matt in contact with the fixed cathodeactive material and configured to retain electrolyte.
 11. The cell ofclaim 10 wherein the separator arrangement includes an ion exchangemembrane in contact with the anolyte.
 12. The cell of claim 10 whereinthe anolyte is a liquid or liquid slurry.
 13. The cell of claim 10wherein the fixed cathode active material is a paste.
 14. The cell ofclaim 10 wherein the fixed cathode active material comprises nickelhydroxide/nickel oxyhydroxide.